"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
:

When will my boat run fastest: 'Free' running propeller or
fixed/locked propeller? ... Simple question, complicated
answers, I understand ...


When you replace the prop with a folding prop that has nearly zero drag.
It does make a difference. I'm not crazy about a prop with so much
underwater mechanical parts, myself. Those little critters with the little
shells must be of some nuisance to a folding prop with cracks in them.

Freewheeling would seem to produce less drag than it being locked up
dragging, with no load on the prop. Ever notice how quick the dingy stops
when the outboard motor just locks up as opposed to drops to idle speed
still turning the prop slowly?

I'm also told some transmissions will not tolerate freewheeling. Case in
point is when we got this "new-used" Perkins 4-108 from another boater, the
transmission on it was much smaller than the original one in Lionheart on
her old Perkins 4-108. The mechanics said to keep this "fluid drive"
larger transmission because it was made to freewheel for the alternator.
The small transmission was not. I've never seen why, though, and don't
know why.

Oh oh...this is getting too long, again....sorry.

Thank you Roger - your stamina is impressive - thanks! ... I
start to get your point - Sorry it took so long. Coming from
Denmark, where the water is around 13 degrees Celcius these
days, this is a very important message to all sailers: Get
out and sail, and lock your propeller, so we soon can come
out swimming in warmer waters! ... ;-)) ... No Roger you
don't have to give me a lecture in how many sailors we need
in order to increase the temperature in the waters around
Denmark by ten degrees ... you have been very helpful so far
.... thank you!

--
Flemming Torp



"Roger Long" skrev i en meddelelse
...
Your intuition is wrong. You never loosen the grip, you
just change to a different kind of grip. Ever notice how
hot brakes get? That's because they are turning all that
energy into heat. When you let the prop go, it is still
restrained by the friction of the bearings and oil in the
transmission. They get warmer because they are turning
the energy being produced into heat. That gets reflected
in drag on the boat.

When the prop is locked, the shaft break, clutch, or
whatever is holding it doesn't get hotter. What gets
hotter is the water flowing past the blades. That energy
production gets reflected in drag on the boat as well but
there is less of it at normal sailing speeds and
freewheeling shaft rpm.

--

Roger Long



"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
message
. ..


My intuition tells me that when you ' loosen the grip' on
the propeller shaft and let the propeller turn freely, it
reduces the drag on the boat. Right or wrong?

--
Flemming Torp

"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
:

My intuition tells me that when you ' loosen the grip' on
the propeller shaft and let the propeller turn freely, it
reduces the drag on the boat. Right or wrong?



It'd be real easy to test. Get one of those plastic props for a small
outboard, put it on a shaft. Pull it loosely behind the boat,
FREEWHEELING, with no load (which produces no work) using a simple fish
weighing scale to measure its drag. Then, lock it to the shaft so it can't
turn and drag it at the same speed, yet again.

Wanna bet the locked prop draggin' through the water creates lots more drag
than the one locked that can't turn?

Take the dingy out for a spin. Run it wide open then drop the engine into
neutral, freewheeling the prop, and see how long it takes to stop dead.
Crank it back up and run it wide open again. This time, leave it in gear
and just pull the safety lanyard making it lock the prop dead still.
Retime how long it takes it to stop. More the drag, the quicker the stop.
You'll find it stops MUCH quicker pulling that STALLED prop through the
water than one FREEWHEELING.

As Lionheart's freewheeling shaft alternator is TURNED ON to produce power
(producing torque on the alternator shaft), it SLOWS the boat as the
alternator SLOWS THE PROP. The heavier it pulls (more torque produced),
the more it slows the boat and prop. Freewheeling props are producing a
minimal amount of torque...and work with no or little load...as load
increases, to the point of being stalled at maximum torque, the drag-
converted-into-torque INCREASES, not decreases!

If you were to spin the prop faster than its drag is capable of, you will
pass through a point of ZERO DRAG just at the point where increasing the
speed of the prop PRODUCES THRUST. So, as prop speed DECREASES, drag
INCREASES! As prop speed INCREASES, it passes through zero drag at the
point where it starts to produce thrust by turning it even faster!

I'm not a physicist, but I play one on Usenet....(c;
Your assignment for tomorrow's class is pages 287 through 312. Do the
workbook exercies on workbook pages 42-43 for turn in. The test will be on
Friday at 2PM.

It might also be a good time to point out that the HELICOPTER rotor CHANGES
DIRECTION as the chopper crashes. It is FORCED in the OPPOSITE direction
from freewheeling to provide DOWNDRAFT to hold the craft aloft by the
engine. As it decends freewheeling, unless you can reverse the pitch of
the rotor, the RISING air through it will make it spin in the opposite
direction.....making it not relevant to any of our discussion here as props
are fixed pitched and already going in the direction of flow caused by
thrust.

Geez....

"Roger Long" skrev i en meddelelse
...

OK, here is the answer you are looking for.

Unless you have a highly unusual powertrain set up and
strangely pitched prop, determine the position in which
the most blade area is shadowed by keel and hull. Mark
the shaft inside. Stop the shaft in that position. Sail
the boat. It's very unlikely you'll go faster doing
anything else.
--

Roger Long





Now we are getting close to 'basics' Roger ... but, but ...
as I wrote in the introduction, it has so far been very
difficult to get hard evidence from the log when trying to
let the propeller run and have it locked, as the speed of
the boat is a function of so many things, and I'm convinced
that there is not a big difference - so may be my question
is of a more theoretical type, as reliable data are hard to
get in the real world ... In a bassin, it might be easier
.... I have seen som reports, where different kinds of
propellers - folding with two blades, folding with three
blades, fixed with three baldes etc. were compared ... and
the result indicated differences in 'thrust' and in speed
up to between ½ - 1 in worst case ... But I have not seen
any reports on the comparison between a locked and a free
wheeling propeller ... but I have certainly got a lot of
input ... also from the aviation world, that I know nothing
about ... thank you.

But your final proposal is very logical, operational and
easy to implement ... when the water gets warmer, we might
do what you have recommended ... or do as Larry - use the
energy coming from the rotating propeller - og invest in a
folding propeller ... time will show, and thank you so much
for your keen interest in learning me some physics ...

"Larry W4CSC" skrev i en meddelelse
...
"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
:

My intuition tells me that when you ' loosen the grip' on
the propeller shaft and let the propeller turn freely, it
reduces the drag on the boat. Right or wrong?



It'd be real easy to test. Get one of those plastic props
for a small
outboard, put it on a shaft. Pull it loosely behind the
boat,
FREEWHEELING, with no load (which produces no work) using
a simple fish
weighing scale to measure its drag. Then, lock it to the
shaft so it can't
turn and drag it at the same speed, yet again.

Wanna bet the locked prop draggin' through the water
creates lots more drag
than the one locked that can't turn?

Take the dingy out for a spin. Run it wide open then drop
the engine into
neutral, freewheeling the prop, and see how long it takes
to stop dead.
Crank it back up and run it wide open again. This time,
leave it in gear
and just pull the safety lanyard making it lock the prop
dead still.
Retime how long it takes it to stop. More the drag, the
quicker the stop.
You'll find it stops MUCH quicker pulling that STALLED
prop through the
water than one FREEWHEELING.

As Lionheart's freewheeling shaft alternator is TURNED ON
to produce power
(producing torque on the alternator shaft), it SLOWS the
boat as the
alternator SLOWS THE PROP. The heavier it pulls (more
torque produced),
the more it slows the boat and prop. Freewheeling props
are producing a
minimal amount of torque...and work with no or little
load...as load
increases, to the point of being stalled at maximum
torque, the drag-
converted-into-torque INCREASES, not decreases!

If you were to spin the prop faster than its drag is
capable of, you will
pass through a point of ZERO DRAG just at the point where
increasing the
speed of the prop PRODUCES THRUST. So, as prop speed
DECREASES, drag
INCREASES! As prop speed INCREASES, it passes through
zero drag at the
point where it starts to produce thrust by turning it even
faster!

I'm not a physicist, but I play one on Usenet....(c;
Your assignment for tomorrow's class is pages 287 through
312. Do the
workbook exercies on workbook pages 42-43 for turn in.
The test will be on
Friday at 2PM.

It might also be a good time to point out that the
HELICOPTER rotor CHANGES
DIRECTION as the chopper crashes. It is FORCED in the
OPPOSITE direction
from freewheeling to provide DOWNDRAFT to hold the craft
aloft by the
engine. As it decends freewheeling, unless you can
reverse the pitch of
the rotor, the RISING air through it will make it spin in
the opposite
direction.....making it not relevant to any of our
discussion here as props
are fixed pitched and already going in the direction of
flow caused by
thrust.

Geez....


Thank you for proposing an interesting experiment ... I will
try to set up this experiment during the summer holidays ...

In the meantime, I must admit, I'm getting pretty much
confused ... I have just appreciated and accepted Roger
Longs 'lecture' on drag and rotation speed etc., where the
conclusion was: The locked propeller gives the maxium speed
compared to the freewheeling propeller ... And now, you
testify just to the opposite ...

My intuition was exactly as you write - I quote: Wanna bet
the locked prop draggin' through the water creates lots more
drag than the one locked that can't turn? Unquote. I think I
understand what you mean, but being a Dane, and having read
it quite a few times makes me a little uncomfortable - is
the sentence correctly phrased?

The beauty of your proposed experiment is, that it is very
operational with a little plastic propellerthing and the
weight from my wifes kitchen, a string and a piece of wood.
And you can repeat the experiment several time under
different conditions ... I will have to find out have to
keep the propeller from turning and at the same time measure
the drag on the weight, without affecting the weight
measurement ... I don't have a motor on the dinghy ...

I had serious problems understanding the helicopter analogy
.... and the way you phrase the case is the way, my intuition
saw the situation - I quote: It might also be a good time
to point out that the HELICOPTER rotor CHANGES DIRECTION as
the chopper crashes. It is FORCED in the OPPOSITE direction
from freewheeling to provide DOWNDRAFT to hold the craft
aloft by the engine. unquote. Therefore, I do not see, that
this analogy explains anything related to my question.

May be an old quotation is in place now: I'm still confused,
but - hopefully - at a higher level ??? As to the
assignment, I'm afraid I forgot my textbook in the office,
and I will be working from other places the rest of the week
.... sorry!

I'm 'afraid' this debate is not over yet, but you have given
me inspiration to make some funny experiments, that might
give me and my brother in law a clear and convincing answer,
so we can settle our little dispute ... thankyou!

--
Flemming Torp

I'm sory, but I can only see one picture in
alt.binaries.pictures.sports.ocean ... Am I missing
something?

--
Flemming Torp



"Larry W4CSC" skrev i en meddelelse
...
"Roger Long" wrote in
:

Gee, isn't this kind of "niggling and perfectionist", to
quote a well
respected rec.boats contributor?


Oh, you'd have a fit if you looked into that bilge.
There's dishwater,
some oil, some rust, a few tools too deep to reach even
with the magnet,
how awful! It's a boat....not house beautiful.
Everything from the sinks,
shower, everything but the head, dumps in her bilge to be
pumped overboard
WITHOUT those nasty thru-hull fittings rotting away...(c;

Look at the next picture. This is the NEW engine Cap
bought from a guy in
NC I met on this newsgroup. It's a pullout. See? We
didn't even paint
it! Looks awful...runs fantastic. The original looked
worse. It had over
8000 hours on it. This "new" one is only up to 900 hours,
now. Cap'n
Geoffrey couldn't even destroy it trying to start it full
of seawater when
that stupid water injection line to the dripless packing
he had a shipyard
install BACKED UP seawater into the exhaust ports. Try
sailing up Ponce
Inlet S of Daytona Beach in the rush of an outgoing tide
past the
lighthouse and seawall so the tow operator can drag you
all the way to
Daytona Marina. Scary stuff that day. Cutter Doc did a
great job pickling
the engine. It looked like we pumped the Exxon Valdez oil
slick out of the
crankcase...(c;

These pictures are old. I need to carry my camera down,
now that she's
been fitted out, and take some new pictures in her. I'm
usually too busy
when Geoffrey is around working on his to-do list...(c;
He finally gave up
trying to pay me. He asked what I wanted for all my work.
I told him,
"That's easy. Just take me with you." It's worked out
great for both of
us....(c;

"Larry W4CSC" skrev i en meddelelse
...
"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
:

When will my boat run fastest: 'Free' running propeller
or
fixed/locked propeller? ... Simple question, complicated
answers, I understand ...


When you replace the prop with a folding prop that has
nearly zero drag.
It does make a difference. I'm not crazy about a prop
with so much
underwater mechanical parts, myself. Those little
critters with the little
shells must be of some nuisance to a folding prop with
cracks in them.

Freewheeling would seem to produce less drag than it being
locked up
dragging, with no load on the prop. Ever notice how quick
the dingy stops
when the outboard motor just locks up as opposed to drops
to idle speed
still turning the prop slowly?

I'm also told some transmissions will not tolerate
freewheeling. Case in
point is when we got this "new-used" Perkins 4-108 from
another boater, the
transmission on it was much smaller than the original one
in Lionheart on
her old Perkins 4-108. The mechanics said to keep this
"fluid drive"
larger transmission because it was made to freewheel for
the alternator.
The small transmission was not. I've never seen why,
though, and don't
know why.

Oh oh...this is getting too long, again....sorry.

I'm still learning - and reading with great interest ... I
just wonder whether Roger is in agreement ;-))

--
Flemming Torp

In article ,
says...

My answer would be the same as yours and also that if you have a two
blade prop, it should be locked in line with the keel if it is
possible to determine where that is etc.

Well, next time you haul you mark the shaft inside the boat to indicate
when the prop is up and down behid the keel or skeg or whatever. After
twenty years, I might yet get around to doing that.

In our case, the freewheeling prop made so much noise that one of the
first things we did was get a feathering prop. We do have evidence
that feathering the prop increases our sailing speed, in addition to
being quieter.

Ours doesn't freewheel in reverse. And the cost of a feathering prop really
put me off.

In article ,
says...


On Mon, 06 Jun 2005 08:01:55 -0400, Gogarty said:

A freewheeling propeller creates more drag than a locked on.. Just
consider a helicopter. Engine out and rotors freewheeling, the aircraft
will go down safely. Rotors locked and it drops like a stone.

Bad analogy. In a helicopter when the rotors are freewheeling after the
engine dies they're still rotating in a direction that generates lift.

Well yes. That was my point. But if somehow they get locked and don't
rotate. negligible lift. About like a stone, which has some lift

In article ,
says...


On Mon, 6 Jun 2005 13:06:28 -0400, Mike G said:

I just have to ask. In what way is it a bad analogy?

Possibly you are thinking the freewheeling prop would somehow generate
some forward motion. Not likely or you would have a perpetual motion
machine.

Those with an understanding of basic physics will understand my point. It's
clear that a detailed explanation to you would be pointless, as you would
have figured it out by now if you had the basic understanding.


Oh dear. Here we have the old scientist vs. engineer argument. The asymtotic
approach vs. close enough is good enough.